In a background art, there is known an energy dispersive spectroscopy (EDS) in an element analysis, an impurity inspection or the like using a semiconductor, which is characterized in capable of carrying out an element analysis in a short period of time in a wide energy range in the element analysis, the impurity inspection or the like. However, the energy resolution of the energy dispersive spectroscopy depends on an energy gap provided to the semiconductor, and therefore, the energy resolution cannot be made to be equal to or smaller than 100 eV.
Hence, a superconducting X-ray detector is expected as a detector promoting a function of an energy resolution and also having a function of a high counting rate.
For example, a superconducting transition edge sensor type calorimeter constituting one of a superconducting X-ray detector is referred to as TES (Transition Edge Sensor) since the calorimeter utilizes a superconducting transition edge producing a large resistance change relative to a small temperature change (hereinafter, described as TES).
TES comprises a temperature detector for sensing a temperature change by heat generated in accordance with absorption of an X-ray, and a heat link used for escaping the heat generated at inside of the temperature detector to a support board.
When an X-ray is incident on an absorbing member in a state of driving the temperature detector by a constant voltage, a temperature at inside of the temperature detector rises, and a resistance of the temperature detector is rapidly increased by the temperature rise. By increasing the resistance value, a value of a current flowing at inside of the temperature detector is reduced.
A relationship between a current displacement (ΔI) by a reduction in the current value and an energy (E) of X-ray incident on TES can be expressed by the following equation.
[Equation 1]E=ΔIVnτeff  (1)
In the relationship, notation Vn designates a drive voltage, notation τeff designates a time constant of a current pulse.
Therefore, the energy of the incident X-ray can be calculated by measuring the current displacement.
Further, an energy resolution (ΔE) of TES can be expressed by the following equation.
[Equation 2]ΔE=2.355ξ√{square root over (KBT2C)}  (2)
In the equation, notation KB designates the Boltzmann constant, notation T designates an operational temperature, notation C designates a heat capacity, notation ξ designates a parameter depending on a sensitivity of the superconducting X-ray detector, and when the sensitivity of the temperature detector is designated by notation α, the following relationship is established.ΔE∝√{square root over ( )}(KBT2C/α)  (3)
It is necessary therefrom that in order to promote the energy resolution, the sensitivity is increased and the operational temperature is reduced.
Here, the operational temperature is determined by a function of a refrigerator for cooling the superconducting X-ray detector, and a currently obtainable cooling function of a dilution refrigerator or an adiabatic demagnetization refrigerator is 50-100 mK. Therefore, a transition temperature of the temperature detector is set to be 100 mK-200 mK (refer to Nonpatent Reference 1).
Nonpatent Reference 1: K. D. Irwin and other 8 person, Superconducting transition-edge-microcalorimeter x-ray spectrometer with 2 eV energy resolution at 1.5 keV, “Nuclear Instruments and Methods in Physics research A”, US, American Physics Society, 2000, 444, P. 145-150